Single Tuberculin Test Research Articles

Pulmonary Tuberculosis andMycobacterium bovis,Uganda

To the Editor: In 2005, prevalence of human tuberculosis (TB) in Uganda was 559 cases/100,000 population (1). In 2002, the average number of extrapulmonary TB cases in humans, considered a crude indicator of the level of bovine TB, was 7.5% of TB cases for Uganda and 6% for Mbarara district, the main Ugandan milk basin (2). Worldwide, the proportion of human cases caused by Mycobacterium bovis has accounted for 3.1% of all forms of TB (3). Although zoonotic TB is more often reported as an extrapulmonary disease, recent publications report that 0.4%–10% of sputum isolates from patients in African countries are M. bovis (3). These studies, however, give little information about the cattle environment. A 2002 survey of dairy cattle in Mbarara district reported that 74% of herds and 6% of individual animals were reactive to the single tuberculin test (4). However, this test does not differentiate between Mycobacterium species involved. We therefore explored whether M. bovis might be a major threat to human health in this region. From September 2004 through January 2005, we surveyed 658 patients who had been admitted to the Mbarara University Teaching Hospital TB ward after positive bacterial findings for at least 3 sputum smears or positive chest radiographs for smear-negative patients. Of 90 randomly selected patients, only 70 samples were available for analysis to differentiate the species in the M. tuberculosis complex; the other samples were excluded because of contamination, lack of mycobacteria growth on culture, or postal delay in transportation of sample. The questionnaire asked about patients’ demographic data (including occupation), association with cattle, and milk consumption habits. Genomic DNA was extracted from the pellet culture of Middlebrook 7H9 broth (Difco; Cergy, France) as described previously (5). DNA samples were used to carry out PCRs and hybridization processes; we used the GenoType MTBC kit (Hain Lifescience GmbH; Nehren, Germany) for differentiation in the M. tuberculosis complex, especially between M. tuberculosis and M. bovis species (6). Questionnaire responses showed that 27/64 (42.2%; 6 did not answer) patients had a history of raw milk consumption; nevertheless, 20/24 (83%; 3 did not answer) reported that they boiled fresh milk before consuming it, as did 54/60 (90% of all patients; 10 did not answer). Eating undercooked or raw meat was reported by 91% of the patients. Most patients were adult males (ratio 2.14:0.97 male:female for the district population); 8.6% were <18 years old (56% in the district); and average number of persons in household was 5.7 vs. 4.8 for the district (7). Of the samples, 8.6% were from extrapulmonary sites. After amplification and hybridization of sample DNA, 69 samples were found to be M. tuberculosis, and 1 was not a Mycobacterium species. Our sampling method would detect at least 1 case of M. bovis in n patient specimens if the prevalence of bovine TB was > p(0.033%) according to the formula in which a is the first order error (5%): Because of the change in sample size, the limit prevalence was redetermined by using the inverse of the formula above: If at least 1 sample was positive for M. bovis, the prevalence of bovine TB among patients would be >4.2%. However, the prevalence of M. bovis was <4.2% and confirmed the low-level involvement of M. bovis in human TB in Mbarara district. These findings are consistent with previous work in Uganda’s capital, Kampala, and in other African or Asian countries (2,8,9). The estimation of extrapulmonary cases among all TB cases (95% confidence interval 2%–15.2%) did not differ from the official estimate. We can add, using the second formula shown above, that among the 6 extrapulmonary TB cases, the prevalence of M. bovis is <39.3%. Our results come from a population in a highly rural area (91.5% of the population in Mbarara district) (7), where the high prevalence of animal TB has been reported. These results could be explained by the patients’ consumption habits, which reduce the risk for contamination. Even if bovine TB could also be found in other farm or wild animals, it seems to have a minor effect on public health. Zoonotic TB appeared to not be a major public health problem in Mbarara district. However, this finding could also result from underdiagnosis of extrapulmonary TB, from prevalence of M. tuberculosis being so high that in proportion M. bovis is a minor problem, or from rural populations’ difficult access to TB diagnosis (directly observed therapy case detection rate in Uganda in 2005 was 37%) (1).

PRELIMINARY OBSERVATIONS ON MYCOBACTERIUM SPP. IN DAIRY CATTLE IN ECUADOR

This study evaluated bovine tuberculosis in Mejia canton, a major dairy cattle production region in Ecuador. Randomly selected cattle (1,012 from 59 farms) classified according to herd size were tested by the single tuberculin test (STT). Sixty days later, positive reactors were tested again by the comparative tuberculin test (CTT). In addition, tissue samples from two STT-CTT-positive reactors detected on a farm were obtained in a local slaughterhouse and analyzed bacteriologically. A total of 4.24% of the cattle were positive in the STT and 3.85% were positive in the CTT, with the highest number (7.95%) in large herds versus 3.4% in medium herds and 0.3% in small herds. Mycobacterium bovis was isolated from mesenteric lymph nodes and lungs of one animal. A 16S ribosomal RNA-based polymerase chain reaction confirmed culture results and differentiated mycobacteria other than M. tuberculosis. This study confirms the zoonotic importance of tuberculosis in Ecuadorian dairy cattle with herd size likely to be a crucial parameter in the prevalence of the disease. The implementation of a national control program is necessary and should be based on the detection of positive cattle by STT in combination with CTT.

Problems associated with tuberculosis and brucellosis skin-test methods in northern Cameroon

Eight hundred and ninety zebus from the north and far-north provinces of Cameroon were tested with two tuberculin assays to estimate the effect of infection by atypical mycobacteria on tuberculosis diagnosis in the region. Six hundred and seven of these animals were tested simultaneously against brucellosis with a delayed hypersensitivity test to brucellin (DHTB) and three standard serological assays as a comparison of the two classes of tests. The results demonstrated that only one quarter of the animals which were designated as tuberculous by the single tuberculin test were considered tuberculous by the comparative tuberculin test (CTT). For 34% of the CTT-reactive animals, borderline reactions were obtained and the results of the tests were uncertain. With regard to brucellosis, the relative sensitivity of the DHTB was 33%; the relative specificity was 96%. The limitation of the delayed hypersensitivity and serological methods are discussed. The most sensitive diagnostic procedure is a combination of both tests, where subjects are scored as positive if they are positive to either or both tests. The DHTB presents the advantage of requiring neither laboratory facilities nor animal identification.

'Boosted' Tuberculin Reactions Among Cambodian Refugees

To the Editor.— We enjoyed the timely report by Drs Catanzaro and Moser (1982;247:1303) of their observations regarding the health status of various ethnic groups of Indochinese refugees. These authors noted a positive tuberculin skin test result in 57% of 356 Cambodian refugees screened at the Center for Indochinese Health Education, University of California, San Diego Medical Center. It is probable that the rates of tuberculin reactivity found would be different had testing been performed that would allow for inclusion of refugees who might have demonstrated the "booster effect." 1 The Jefferson County (Alabama) Department of Health has provided health screening for more than 200 Vietnamese and Cambodian refugees since October 1980. A positive tuberculin test result (single tuberculin test performed) occurred at an average rate of 50% among all Indochinese. Following the report from New York 2 in late 1981 describing apparent tuberculin conversion among refugees, we conducted "two-step"

A single tuberculin test for epidemiological use:A comparison of the mantoux and heaf tests: A report to the Research Committee of the BritishTuberculosis Association by their Tuberculin Sub-Committee

A single tuberculin test for epidemiological use:A comparison of the mantoux and heaf tests: A report to the Research Committee of the BritishTuberculosis Association by their Tuberculin Sub-Committee

A single tuberculin test for epidemiological use: Comparison of four tests: A report to the research committee of the British Tuberculosis Association

A single tuberculin test for epidemiological use: Comparison of four tests: A report to the research committee of the British Tuberculosis Association